The present invention relates to an internal-combustion engine comprising a rocker lever valve gear which, in a cylinder head, and actuated by a camshaft by an end of a rocker lever, controls at least one charge cycle valve, with the abutment point of the rocker lever being changeable by the swivelling of a shaft.
The SAE Paper 88 07 30 "Variable Valve Action Through Variable Ratio Rocker Arms", 1988, shows an internal-combustion engine which comprises a rocker lever valve gear with a variable valve lift, in which a lower camshaft, by way of a push rod, actuates a rocker lever which acts upon a charge cycle valve by one of its ends. The rocker lever has an internally toothed guiding connecting link in which a correspondingly toothed shaft rolls off. The engaging teeth represent the abutment point of the rocker lever. By rotation of the shaft, this shaft rolls off inside the connecting link of the stationary rocker lever so that the abutment point can be changed. As a result, the leverages at the rocker lever change in such a manner that, when the cam lift is constant, a variable valve lift is created as a function of the position of the abutment point.
Disadvantages of the above-described solution are the high-expenditure toothing, particularly in the rocker levers, as well as the superimposed rotatory and translational movement of the shaft.
An object of the present invention is to provide, while the cam lift is constant, a variable valve lift in an internal-combustion engine comprising a rocker lever valve gear.
This and other objects are achieved by the present invention which provides an internal-combustion engine which includes at least one charge cycle valve and a rocker lever valve gear in a cylinder head and which is actuated by a camshaft. The rocker lever valve gear has a rocker lever with an end that controls the at least one charge cycle valve. The rocker lever also has a changeable abutment point and an arc shaped longitudinal part. A pivotable control shaft and abutment receiving devices are coupled to the control shaft so as to be pivotable together with the control shaft. The longitudinal part of the rocker lever is in contact with the abutment receiving devices at the abutment point. The abutment point of the rocker lever is changed by pivoting the control shaft.
The rocker lever of the present invention has a circular-arc-shaped longitudinal part, along which the abutment point can be shifted. This shifting takes place by a joint swivelling of abutment receiving devices arranged on a shaft. Advantageously, a shifting of the abutment point is achieved by a simple rotation of the shaft. As a function of the curvature of the longitudinal part or of the angle of rotation of the shaft, as a result, the valve lift can be varied without any complicated design of components.
Geometrically simple conditions exist which are favorable with respect to the flux of forces if the radius of curvature of the longitudinal part extends from the longitudinal center axis of the shaft to the longitudinal part, as in an embodiment of the present invention. In a further embodiment, the abutments are hydraulic valve clearance compensating elements which are arranged in the abutment receiving devices.
For a compact construction of modern internal-combustion engines, an embodiment of the present invention provides that the cams of the camshaft are applied at a point of the rocker lever which is situated between the fixed bearing on the upper end of the charge cycle valve and the movable abutment point.
In an embodiment of the present invention, the guiding of the rocker lever on the charge cycle valve takes place rotatably on a shaft which is disposed in parallel to the camshaft and is fastened to the charge cycle valve. On the opposite free end, a guiding takes place in a sliding manner between parallel contact surfaces. The variation of the valve lift takes place as a function of parameters of the internal-combustion engine, such as load and rotational speed, by a control element which is applied to a pivoted lever which is non-rotatably arranged on the shaft. This control element may, for example, comprise pistons which are acted upon hydraulically and are applied to the pivoted lever. In this case, the oil pressure can be utilized which already exists in the cylinder head. As an alternative, the control element may comprise an electric motor or magnet or a pneumatic cylinder which rotates the shaft continuously as a function of, for example, the intake pipe vacuum.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.